Surgical microscopes are covered with a sterile protective covering in order to make possible sterile work with surgical microscopes in operating rooms. The protective covering is a so-called drape. Such protective coverings are available from Microtek Medical, Inc. under reference numeral 4865 CL or from the Pharma-Sept Ltd. under the reference numeral 80-266 SB.
These sterile protective coverings have a viewing opening for the surgical microscope main objective so that the view through the surgical microscope onto the operating area is not affected. This viewing opening is, as a rule, formed by a holding device which is enclosed and sealed by a circularly-shaped cutout of the sterile protective covering. The holding device is attached to the main objective of the surgical microscope and carries a protective element of glass or plastic which covers the main objective of the surgical microscope.
A holding device of the kind referred to above is disclosed, for example, in U.S. Pat. No. 5,608,574. There, a protective covering for a surgical microscope is described wherein a holding device in the form of an insert in the protective covering is provided. This insert has a radial flange extending outwardly. This flange is glued to the protective covering and is enclosed by an edge of a viewing opening. The flange has a circularly-shaped recess having several ribs at its inner wall which extend in a longitudinal direction. The inner diameter of the flange is adapted to the outer diameter of a surgical microscope main objective. The flange can be pushed onto a main objective of a surgical microscope in order to hold friction-tight on the outer wall of the main objective under the clamping action of the ribs. At its lower side, the holding device is cut at an angle and there has a receptacle for a transparent cover element which protects the surgical microscope main objective against contamination and makes possible also the sterile work with the surgical microscope.
The cover element is configured to be disc shaped. The cover element has projecting ribs which, with projections at the lower side of the holding device, make possible a connection of cover element and holding device. This connection has the form of a bayonet connection and can be opened and closed by turning the cover element relative to the holding device.
A holding device for a sterile protective covering on a surgical microscope main objective is described in U.S. Pat. No. 6,024,454 and this holding device includes an adapter ring which is pushed onto the main objective of the surgical microscope. A clamping screw is provided for adjusting the clamping force for the adapter ring mounted on the main objective of the surgical microscope. A spring biased O-ring is provided on the outer side of the adapter ring and a ring connected to the sterile protective covering is pushed onto this O-ring in order to provide a friction-tight hold. A cover glass can be attached by means of a bayonet connection at the lower side of the ring tightly connected to the sterile protective covering.
U.S. Pat. No. 6,257,730 discloses a sterile protective covering having a holding device for covering a surgical microscope with this holding device being made of elastomer. This holding device is placed about the main objective of the surgical microscope in order to hold the protective covering friction-tight or force-tight.
U.S. Pat. No. 5,467,223 discloses a sterile protective covering having a holding device for attaching to a main objective of a surgical microscope. The holding device includes an adapter unit which can be threadably engaged in a housing for the surgical microscope main objective. Furthermore, U.S. Pat. No. 5,467,223 discloses a holding device which includes an adapter unit which can be threadably mounted outside on a surgical microscope main objective. This adapter unit is configured to have an annular shape and preferably comprises a rigid material such as aluminum. In the holding device, a ring element made of elastomer material is provided which is tightly connected to the sterile protective covering. This ring element can be pushed over the adapter unit in order to hold the protective covering on the surgical microscope in the region of the main objective thereof.